Method and apparatus to form a planarized Cu interconnect layer using electroless membrane deposition

ABSTRACT

A planarized conductive material is formed over a substrate including narrow and wide features. The conductive material is formed through a succession of deposition processes. A first deposition process forms a first layer of the conductive material that fills the narrow features and at least partially fills the wide features. A second deposition process forms a second layer of the conductive material within cavities in the first layer. A flexible material can reduce a thickness of the first layer above the substrate while delivering a solution to the cavities to form the second layer therein. The flexible material can be a porous membrane attached to a pressurizable reservoir filled with the solution. The flexible material can also be a poromeric material wetted with the solution.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of semiconductorfabrication and more particularly to methods and apparatuses for formingconductive materials with planarized surfaces within features defined ina substrate, the features having widely different dimensions.

2. Description of the Prior Art

FIG. 1 provides a cross-section of a partially fabricated semiconductordevice 100 including a substrate 102 and a conductive layer 104. Thesubstrate 102 is typically a dielectric material and can includetrenches of various dimensions such as wide trench 106 and narrowtrenches 108. In addition to trenches, the substrate 102 can includeother similar features of various dimensions such as vias (not shown).Such features in the substrate 102 are commonly fabricated through wellknown photolithography processes. The conductive layer 104 is typicallya highly conductive metal such as copper (Cu). After further processing,the conductive layer 104 is removed down to the level of the top surfaceof the substrate 102 such that the conductive material remaining in thetrenches 106, 108 and other similar features are electrically separatedby the substrate 102 in the finished semiconductor device.

The conductive layer 104 is commonly formed through electroplating withan electroplating solution that contains the metal to be plated.Electroplating is desirable because it is a rapid method for depositinga metal on a surface. One of the drawbacks of electroplating, however,is that voids frequently form in the more narrow features, such astrenches 108, and such voids can cause failures in the finishedsemiconductor device. Certain additives when added to the electroplatingsolution can promote rapid filling of the narrow features and preventvoid formation, however, these same additives tend to retard thedeposition rate in generally flat areas such as the surfaces betweentrenches 106, 108 and along the bottom of the wide trench 106.

Accordingly, by the time the conductive layer 104 completely fills thelarger features, such as wide trench 106, a substantial thickness, oroverburden 10, covers the remainder of the substrate 102. Further, sincethe additives to the electroplating solution promote rapid filling ofthe narrow features while retarding it in generally flat areas, an areaof superfill 112 can also develop above the level of the top of theoverburden 110 over narrow features, as shown in FIG. 1. It will beappreciated that to remove the conductive layer 104 down to the level ofthe top surface of the substrate 102 requires removing three differentthicknesses of material. Unfortunately, the planarization techniquesknown in the art are poorly suited to such a task, and generally causedishing 200 over larger features, such as shown over large trench 106 inFIG. 2.

One solution is to electroplate further than is shown in FIG. 1 suchthat the thickness of the overburden 10 is greater over the entiresubstrate 102. If carried far enough, the thickness of the overburden110 tends to even out over the entire substrate 102. The overburden 110can then be uniformly planarized down to the level of the top surface ofthe substrate 102. This solution, however, wastes material and is timeconsuming.

Therefore, what is desired is a method of forming a conductive layer 104with an overburden 110 that has an essentially planar surface.

SUMMARY

The invention provides a method for producing a planarized surfaceincluding providing a substrate, forming first and second layers, andplanarizing the first and second layers. The substrate has a narrowfeature and a wide feature defined therein, and the first layer isformed above the substrate such that it fills the narrow feature, atleast partially fills the wide feature, and has a cavity defined thereinthat is aligned with the wide feature. The second layer is formed in thecavity while the first layer is contemporaneously planarized. The firstand second layers are then planarized together.

In some embodiments forming the second layer while planarizing the firstlayer includes contacting a flexible material with the first layer, andintroducing a relative lateral motion between the flexible material andthe first layer. In some of these embodiments the relative lateralmotion includes a rotational component, a vibrational component, and/oran orbital component. In those embodiments in which the first layercompletely fills the wide feature, planarizing the first and secondlayers can include completely removing the second layer. In otherembodiments planarizing the first and second layers does not completelyremove the second layer. In some embodiments planarizing the first andsecond layers includes a stress-free planarization or achemical-mechanical planarization. In some embodiments planarizing thefirst and second layers includes exposing the substrate between thenarrow and wide features.

The invention also provides a method for producing a planarized surfacethat includes providing a substrate, forming a first layer, contacting aflexible material with at least a portion of the first layer, forming asecond layer, and planarizing the first and second layers. The substratehas a narrow feature and a wide feature defined therein, and the firstlayer is formed above the substrate such that it fills the narrowfeature, at least partially fills the wide feature, and has a cavitydefined therein that is aligned with the wide feature. According to themethod, the flexible material is used to deliver a solution to thecavity and the second layer is formed from the solution. In someembodiments the solution includes an electroless plating solution, andin some of these embodiments forming the second conductive layerincludes an electroless deposition of a conductive material, such ascopper. In some embodiments the first and second layers are formed ofthe same conductive material. In some embodiments contacting theflexible material with at least the portion of the first layer inhibitsthe deposition of the second layer above an overburden of the firstlayer.

In some embodiments of this method, the substrate can include adielectric material with a dielectric constant less than a dielectricconstant of SiO₂, such as organosilicate glass. In some embodiments, thenarrow feature can have a lateral dimension of about 100 nm or less, andin some embodiments the wide feature can have a lateral dimensiongreater than about 100 nm or of about 500 μm. In some embodiments,forming the first layer includes forming a first conductive layer, andin some of these embodiments forming the first conductive layer includesan electrochemical deposition of a conductive material, such as copper.In some embodiments planarizing the first and second layers includesapplying a stress-free polishing technique.

In some embodiments of this method the flexible material includes aporous membrane such as polyurethane. In some of these embodiments themethod further includes pressurizing a reservoir containing the solutionand adjoining the membrane on a side opposite a side contacting thefirst layer. Also in some of these embodiments the method furtherincludes introducing a relative lateral motion between the porousmembrane and the substrate. In some of the embodiments that includeintroducing a relative lateral motion, the porous membrane is effectiveto polish the portion of the first layer, for example, because theporous membrane includes an abrasive.

In some embodiments of this method the flexible material includes aporomeric material. In some of these embodiments the poromeric materialincludes a closed-cell structure with open pores exposed at a surfacethereof. In some of these embodiments the method further includeswetting the poromeric material with the solution. Also in some of theseembodiments delivering the solution to the cavity can include developinga pressure between the poromeric material and the first layer. In someof these embodiments delivering the solution to the cavity can alsoinclude introducing a relative lateral motion between the substrate andthe poromeric material.

In some embodiments of this method forming the first layer includescompletely filling the wide feature, and in some of these embodimentsthe first layer forms an overfill above the wide feature that extendsabout 10% to about 20% of a depth of the wide feature above a level of atop surface of the substrate. Also in some of these embodimentsplanarizing the first and second layers includes removing the secondlayer. In other embodiments of this method forming the first layerincludes filling less than the entire wide feature, and in some of theseembodiments about 10% to about 30% of a depth of the wide feature isfilled by the first layer. Also in some of these embodiments planarizingthe first and second layers includes removing less than the entiresecond layer.

The invention also provides an apparatus for producing a planarizedsurface. The apparatus includes a wafer support, such as a vacuum chuck,for securing a wafer having an area, a workpiece, an engagementmechanism capable of bringing the workpiece and the wafer into contactwith each other, and means for introducing a relative lateral motionbetween the workpiece and the wafer. The workpiece includes a reservoircontaining an electroless plating solution and having a flexible andporous membrane spanning a side. In some embodiments the reservoir ispressurizable. In some embodiments the porous membrane includes anabrasive.

In some embodiments of this apparatus the porous membrane has an arealess than the area of the wafer. In some of these embodiments the meansfor introducing relative lateral motion includes means for linearlytranslating the workpiece, and in some of these embodiments the meansfor introducing relative lateral motion further includes means forrotating the workpiece around an axis. In some embodiments the means forintroducing relative lateral motion can also include means for rotatingthe wafer support around an axis and/or vibrating the workpiece.

In some embodiments of this apparatus the porous membrane has an areaequal to or larger than the area of the wafer. In some of theseembodiments the means for introducing relative lateral motion includesmeans for rotating the workpiece and/or the wafer support around anaxis.

In some embodiments of this apparatus the porous membrane can bepolyurethane, a fluorocarbon material, a sintered polymeric material, ora ceramic. In some embodiments the porous membrane can have a thicknessbetween about 0.1 mm to about 3.0 mm. In some embodiments the porousmembrane can include an open-cell pore structure. In some embodimentsthe porous membrane can include a number of holes disposed therethrough.Also in some embodiments the porous membrane can include an amount ofporosity between about 5% to about 50%, and in some of these embodimentsthe amount of porosity is between about 10% to about 20%.

Another apparatus of the invention includes a wafer support for securinga wafer, a flexible poromeric material wetted with an electrolessplating solution, an engagement mechanism capable of bringing theporomeric material into contact with the wafer, and means forintroducing a relative lateral motion between the poromeric material andthe wafer. In some embodiments the poromeric material includes apolymeric material, and in some embodiments the poromeric materialincludes a closed-cell structure with open pores exposed at a surface.In some embodiments the poromeric material is in a shape of a continuousloop, a disk, or a rectangle. Also in some embodiments the poromericmaterial includes a raised edge to contain the electroless platingsolution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-section of a partially fabricated semiconductor deviceaccording to the prior art;

FIG. 2 is a cross-section of the partially fabricated semiconductordevice of FIG. 1 after a planarization according to the prior art;

FIG. 3 is a cross-section of a partially fabricated semiconductor deviceaccording to an embodiment of the invention;

FIG. 4 is a cross-section of a substrate for fabricating a semiconductordevice according to an embodiment of the invention;

FIG. 5 is a cross-section of the partially fabricated semiconductordevice of FIG. 4 after one or more optional layers have been formed overthe substrate according to an embodiment of the invention;

FIG. 6A is a cross-section of the partially fabricated semiconductordevice of FIG. 5 after a first conductive layer has been formed over thesubstrate according to an embodiment of the invention;

FIG. 6B is a cross-section of the partially fabricated semiconductordevice of FIG. 5 after a first conductive layer has been formed over thesubstrate according to another embodiment of the invention;

FIG. 7 is a cross-section of the partially fabricated semiconductordevice of FIG. 6A after a second conductive layer 700 has been formedaccording to an embodiment of the invention;

FIG. 8 is a cross-section of the partially fabricated semiconductordevice of FIG. 7 after further planarization according to an embodimentof the invention;

FIG. 9 is a cross-section of the partially fabricated semiconductordevice of FIG. 5 after a first conductive layer has been formed over thesubstrate according to another embodiment of the invention;

FIG. 10 is a cross-section of the partially fabricated semiconductordevice of FIG. 9 after a second conductive layer has been formedaccording to an embodiment of the invention;

FIG. 11 is a cross-section of the partially fabricated semiconductordevice of FIG. 10 after further planarization according to an embodimentof the invention;

FIG. 12 is a cross-section of a partially fabricated semiconductordevice contacting a flexible material according to an embodiment of theinvention;

FIG. 13 is a cross-section of the partially fabricated semiconductordevice of FIG. 12 after a second conductive layer has been formedaccording to an embodiment of the invention;

FIG. 14 is a side elevation view of a partial cross-section of anapparatus for producing a pre-planarized surface according to anembodiment of the invention;

FIG. 15 is a top plan view of the apparatus of FIG. 14 according to anembodiment of the invention;

FIG. 16 is a top plan view of another apparatus for producing apre-planarized surface according to an embodiment of the invention;

FIG. 17 is a top plan view of another apparatus for producing apre-planarized surface according to an embodiment of the invention;

FIG. 18 is a side elevation view of a cross-section of another apparatusfor producing a pre-planarized surface according to an embodiment of theinvention; and

FIG. 19 a side elevation view of another apparatus for producing apre-planarized surface according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention employs two deposition processes in succession to form aconductive layer over a substrate that includes both narrow and widefeatures such that the conductive layer has an overburden with anessentially planar surface, as shown in FIG. 3. Initially, a firstprocess such as electroplating is used to form a first layer of theconductive layer. The first process is discontinued after the narrowfeatures are completely filled. Next, a second process, such aselectroless deposition, is used to form a second layer within cavitiesin the first layer associated with the wide features. The second layeris formed such that it has a top surface that is essentially coplanarwith a top surface of an overburden of the first layer.

In some embodiments a flexible material is brought into contact with thefirst layer during the second process to inhibit deposition on topsurfaces of the overburden so that the thickness of the overburden doesnot appreciably increase while deposition is occurring within cavitiesin the first layer such as a cavity 114 (FIG. 1) in first layer 104 thatis aligned with wide trench 106. A relative lateral motion can also beintroduced between the flexible material and the first layer to furtherinhibit deposition on top surfaces of the overburden. The relativelateral motion between the flexible material and the first layer canalso cause, in some instances, a reduction in the thickness of theoverburden, for example, through polishing. The flexible material can bemade abrasive in order to enhance the rate of overburden removal.

The flexible material also can serve to deliver an electroless platingsolution to the cavities. In some embodiments the flexible material is aporous membrane through which the electroless plating solution ispassed, in some instances from a pressurized reservoir on the oppositeside of the porous membrane. In other embodiments the flexible materialis a poromeric material that is wetted with the electroless platingsolution. Relative lateral motion then can bring the electroless platingsolution to the cavities.

FIG. 4 provides a cross-section of a substrate 102 for fabricating asemiconductor device. The substrate 102 is typically formed over a wafer(not shown), such as a silicon wafer, and can additionally be formedover previously fabricated device layers (not shown). The substrate 102can be a dielectric material such as SiO₂. The substrate 102 can also bea low dielectric constant (“low k”) material, one that has a dielectricconstant less than that of SiO₂, such as fluorosilicate glass (FSG),organosilicate glass (OSG), or highly porous SiO₂. Such low k materialsare increasingly favored in semiconductor device fabrication as theyimpart superior electrical properties to the finished devices. Onecharacteristic common to low k materials, however, is low density andpoor mechanical properties such as reduced hardness and increasedbrittleness. Although the invention is not limited to using low kmaterials for the substrate 102, it will be appreciated that the presentinvention has advantages when the substrate 102 is formed of a low kmaterial, as discussed further herein.

The substrate 102 includes features of various dimensions such as widetrench 106 and narrow trenches 108. While trenches 106 and 108 are usedherein for illustrative purposes, it will be understood that theinvention is equally well suited for substrates that include othercommon features formed into semiconductor substrates, such as vias.Narrow features such as narrow trenches 108 in some embodiments havelateral dimensions of about 100 nm or less, while wide features such aswide trench 106 in some embodiments have lateral dimensions greater thanabout 100 nm and up to about 500 μm. Features such as trenches 106, 108can be fabricated through well known photolithography processes.

FIG. 5 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 4 after one or more optional layers 500have been formed over the substrate 102. One optional layer is a barrierlayer to prevent metal atoms from a later-deposited layer fromeventually diffusing into the substrate 102. The barrier layer can beformed of a material such as Ta or TaN, for example, by chemical vapordeposition (CVD). Another optional layer 500 is a seed layer such as aCu seed layer formed, for example, by physical vapor deposition (PVD).The seed layer can be deposited over the barrier layer, when present, topromote adhesion, provide a conductive surface, and facilitate uniformlayer growth of the subsequent later-deposited layer.

FIG. 6A provides a cross-section of the partially fabricatedsemiconductor device of FIG. 5 after a first conductive layer 600 hasbeen formed over the substrate 102 and over any optional layers 500.First conductive layer 600 is preferably formed of a highly conductivemetal such as Cu. First conductive layer 600 can be formed by anelectrochemical deposition technique such as electroplating. In anelectroplating process a surface to be plated is brought into contactwith an electroplating solution containing ions of the metal to bedeposited. The surface to be plated is then made to be a cathode in anelectrochemical cell. As is well known, the applied voltage across theelectrochemical cell causes the metal ions in the electroplatingsolution to deposit as a metal film on the cathode. In order to preventvoids from forming in the more narrow features, the electroplatingsolution can also contain additives that inhibit void formation. In someembodiments the electroplating solution contains three additives, anaccelerator, a leveler, and an inhibitor. Such electroplating solutionsare commonly referred to as 3-component solutions. Suitable 3-componentelectroplating solutions can be obtained from Shipley Ronal (Freeport,N.Y.).

In some embodiments, the first conductive layer 600 is formed such thatthe narrow features such as narrow trenches 108 are completely filled bythe first conductive layer 600 while the wider features such as widetrench 106 are at least partially filled. For example, as shown in FIG.6A, the wide trench 106 is about half filled by first conductive layer600. In some embodiments about 10% to about 30% of the depth of the widetrench 106 is filled by the first conductive layer 600. Whenelectroplating is used to deposit the first conductive layer 600, thedeposition can be stopped after the narrow features are completelyfilled but before the wider features are completely filled. In theseembodiments, an overburden 602 is thinner than the overburden 110(FIG. 1) and a superfill 604 over narrow trenches 108 is thinner thanthe superfill 112 (FIG. 1). In some instances, by halting the depositionof the first conductive layer 600 just after the narrow trenches 108 arefilled, the superfill effect can be essentially eliminated, asillustrated in FIG. 6B. It can be seen from FIGS. 6A and 6B that firstconductive layer 600 includes a cavity 606 that is aligned with the widetrench 106.

FIG. 7 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 6A after a second conductive layer 700 hasbeen formed within the cavity 606. Second conductive layer 700 is alsopreferably formed of a highly conductive metal such as Cu. In someembodiments the first and second conductive layers 600, 700 are formedof the same conductive material. Second conductive layer 700 can beformed by an electroless deposition technique such as electrolessplating. In an electroless plating process a metal is deposited from anelectroless plating solution, but in contrast to electroplatingtechniques, no external voltage is applied. Instead, as electrolessplating solution including a metal ion species is circulated through thecavity 606, the metal is deposited from the metal ion species byreduction from a reducing agent within the cavity 606 to form the secondconductive layer 700. Suitable electroless plating solutions includeCircuposit™ Electroless Copper 3350 produced by Shipley Ronal (Freeport,NY).

In some embodiments, while the second conductive layer 700 is beingformed within the cavity 606, the superfill 604 and some of theoverburden 602 are also being removed. This can cause the removal ofsubstantially all of the superfill 604 and create a generally planarsurface of the overburden 602. Therefore, as shown in FIG. 7, once thesecond conductive layer 700 is complete in these embodiments, the secondconductive layer 700 has a top surface that is essentially coplanar witha top surface of the overburden 602 of the first conductive layer 600.Together, the top surfaces of the overburden 602 and the secondconductive layer 700 form a pre-planarized surface 702. Methods forlimiting the deposition of the second conductive layer 700 to the cavity606 and for removing the superfill 604 and overburden 602 are discussedelsewhere herein.

FIG. 8 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 7 after removal of the overburden 602 and aportion of the second conductive layer 700. As can be seen in FIG. 8,removing the conductive materials between the tops of trenches 106, 108selectively exposes the substrate 102 between the tops of trenches 106,108 and electrically isolates the conductive materials remaining withinthe trenches 106, 108. The conductive materials within the wide trench106 can form an electrical interconnect, for example, in a completedsemiconductor device. Similarly, the portions of the first conductivelayer 600 remaining in the narrow trenches 108 can form elements of anarray.

Referring again to FIG. 7, the pre-planarized surface 702 allows variousplanarization techniques to be successfully employed to create thepartially fabricated semiconductor device of FIG. 8 without the dishing200 illustrated in FIG. 2. Examples of planarization techniques that canbe employed in the present invention include Chemical-MechanicalPolishing (CMP), Stress-Free Planarization (SFP), and electrochemicalpolishing. Many CMP techniques are well known in the art. SFP techniquesare especially well suited for use where the substrate 102 includes aweak or brittle material, such as OSG or porous OSG, as these techniquesproduce little or no shear forces at the planarized surface. Some SFPtechniques include plasma etching. Some other SFP techniques employ aconventional rotating polishing pad. Some of these techniques rely onvery low applied pressures to reduce shear forces, while others useabrasive-free polishing solutions, and still other techniques combinelow applied pressures with abrasive-free polishing solutions.Additionally, electrochemical polishing techniques can be employed, forexample, by applying a voltage across the substrate 102 through aconductive pad.

In other embodiments, rather than having first conductive layer 600 onlypartially fill the wide trench 106 as in FIGS. 6A and 6B, the widetrench 106 is instead completely filled. In accordance with theseembodiments, FIG. 9 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 5 after a first conductive layer 900 hasbeen formed over the substrate 102 and over any optional layers 500.First conductive layer 900 is preferably formed of a highly conductivemetal such as Cu, and can be formed, for example, by an electrochemicaldeposition technique such as electroplating.

As shown in FIG. 9, the first conductive layer 900 completely fills thewide trench 106. In some embodiments, the first conductive layer 900forms an overfill 902 that extends about 10% to about 20% of a depth ofthe wide trench 106 above the level of the top surface of the substrate102. It will be appreciated that although first conductive layer 900completely fills the wide trench 106, a cavity 904 aligned with the widetrench 106 still exists in the first conductive layer 900. It will alsobe appreciated that in some of these embodiments an overburden 906 issufficiently thick that a thickness of the overburden 906 issubstantially the same over both narrow trenches 108 and over thosesurfaces between the tops of trenches 106, 108, as shown in FIG. 9.

FIG. 10 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 9 after a second conductive layer 1000 hasbeen formed within the cavity 904 (FIG. 9). Second conductive layer 1000is also preferably formed of a highly conductive metal such as Cu, andin some embodiments the first and second conductive layers 900, 1000 areformed of the same conductive material. Second conductive layer 1000 canbe formed, for example, by an electroless deposition technique such aselectroless plating. In some embodiments, as shown in FIG. 10, while thesecond conductive layer 1000 is being formed within the cavity 904, anyremaining superfill and some of the overburden 906 are being removed. Inthese embodiments, once the second conductive layer 1000 is complete,the second conductive layer 1000 has a top surface that is essentiallycoplanar with a top surface of the overburden 906. Together, the topsurfaces of the overburden 906 and the second conductive layer 1000 forma pre-planarized surface 1002.

FIG. 11 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 10 after removal of the overburden 906(FIG. 10) and all of the second conductive layer 1000 (FIG. 10). Thepre-planarized surface 1002 in FIG. 10 allows various planarizationtechniques to be successfully employed to create the partiallyfabricated semiconductor device of FIG. 11 without the dishing 200illustrated in FIG. 2. Examples of planarization techniques that can beemployed in the present invention are discussed elsewhere herein.

FIGS. 12 and 13 illustrate one method for achieving the pre-planarizedsurface 702 of FIG. 7. Specifically, FIG. 12 provides a cross-section ofa partially fabricated semiconductor device, such as that shown in FIG.6A, with a flexible material 1200 contacting a first conductive layer1202. It will be appreciated that the method described with reference toFIGS. 12 and 13 is equally applicable to those embodiments illustratedwith respect to FIGS. 9 and 10. Accordingly, first conductive layer 1202is representative of both first conductive layers 600 and 900.

Flexible material 1200 can serve several functions in the process offorming a pre-planarized surface such as pre-planarized surface 702(FIG. 7) or pre-planarized surface 1002 (FIG. 10). One function offlexible material 1200 is to support a mass transport of material to acavity that will be filled by a second conductive layer such as secondconductive layer 700 (FIG. 7). Similarly, in those embodiments in whichthe formation of the second conductive layer within the cavity createswaste products, flexible material 1200 also can function to support themass transport of the waste products away from the cavities. Anotherfunction of flexible material 1200 in some embodiments is to inhibitgrowth of the second conductive layer in areas other than cavities.Still another function of flexible material 1200 in some embodiments isto selectively reduce the thickness of the first conductive layer 1202by removing superfill effects and by thinning the overburden.

In some embodiments, such as those described with respect to FIGS.14-17, flexible material 1200 supports a mass transport of material to acavity 1204 by providing for the mass transport through its thickness.For instance, flexible material 1200 can be a porous membrane so that asolution, such as an electroless plating solution, can be made to flowtherethrough. A pressurized reservoir (not shown) on one side of theflexible material 1200 can cause the solution to flow through theflexible material 1200 and into the cavity 1204. It will be appreciatedthat any such flexible material 1200 should have a sufficient stiffnessover dimensions comparable to the widest dimension of the cavity 1204(this dimension is commonly referred to as a “planarization length”)such that the flexible material 1200 remains essentially flat over thecavity 1204 instead of bowing into the cavity 1204. At the same time,the flexible material 1200 should be compliant enough that it is able toconform to features having peak-to-peak dimensions greater than theplanarization length. In some embodiments the flexible material 1200provides a planarization length of up to 500 microns. It should be notedthat FIG. 12 is not to scale inasmuch as the bend in the flexiblematerial 1200 between the cavity 1204 and a superfill 1208 has beenexaggerated.

In those embodiments in which flexible material 1200 supports a masstransport of material through its thickness, suitable materials forflexible material 1200 include porous membranes formed of polyurethane,porous or sintered polymeric materials such as polyethylene,polypropylene, and fluorocarbon materials such as Teflon™, and ceramics.In some embodiments the flexible material has a thickness between about0.1 mm to about 3.0 mm. An appropriate flexible material 1200 for aparticular application should be one that is compatible with theintended solution. For instance, the flexible material 1200 should bechemically resistant to the solution. To provide adequate mass transportof the solution through the flexible material 1200, the flexiblematerial 1200 should include a number of channels of sufficientdiameter. An open-cell pore structure provides the channels in someflexible materials 1200, while other flexible materials 1200 areperforated with a number of holes disposed through the flexible material1200 from one side to the other. In still other embodiments holes areadded to an otherwise porous flexible material 1200. Such holes can beproduced by laser drilling, for example. In some embodiments the amountof porosity, whether inherent or added, is between about 5% to about50%, while in other embodiments the porosity is between about 10% toabout 20%.

In other embodiments, such as those described with respect to FIGS. 18and 19, flexible material 1200 supports a mass transport of material toa cavity 1204 by carrying a solution, such as an electroless platingsolution. For instance, flexible material 1200 can be a poromericmaterial such as a polymeric material that has a closed-cell structurewith open pores exposed at a surface. After the surface is wetted by thesolution, relative lateral motion can then be used to deliver thesolution to the cavity 1204.

Another function of flexible material 1200 in some embodiments is toinhibit growth of the second conductive layer in areas other thancavities. It will be appreciated that where broad areas of an overburden1206 or the superfill 1208 are in direct contact with the flexiblematerial 1200 the presence of the flexible material 1200 can inhibitdeposition of the second conductive layer directly or through inhibitionof mass transport in those regions. Relative lateral motion between theflexible material 1200 and the areas of the overburden 1206 can alsoinhibit deposition of the second conductive layer.

Still another function of flexible material 1200 in some embodiments isto selectively reduce the thickness of the first conductive layer 1202by removing superfill effects and by thinning the overburden 1206. Inthese embodiments a relative lateral motion between the flexiblematerial 1200 and the areas of the overburden 1206 is used to thin theoverburden 1206. Thinning can be accelerated through the use ofabrasives. In some embodiments, the flexible material 1200 includes anabrasive that is dispersed throughout such that some of the abrasive isexposed at the surface in contact with the overburden 1206. In otherembodiments, polishing media such as a polishing pad, cloth, or tape isused as the flexible material 1200. In some of these embodiments holescan be added to the polishing media to create additional porosity toallow a solution to be delivered therethrough.

As noted herein, a relative lateral motion can enhance the method of theinvention in many ways. Relative lateral motion can include lineartranslations along one or two axes, reciprocation, vibration, rotation,orbital motion, and the combinations thereof. Examples of relativelateral motions will be discussed in further detail with respect to theembodiments shown in FIGS. 14-19.

FIG. 13 provides a cross-section of the partially fabricatedsemiconductor device of FIG. 12 after a second conductive layer 1300 hasbeen formed within the cavity 1204 (FIG. 12). A pre-planarized surface1302 results from forming the second conductive layer 1300 within thecavity 1204 while contemporaneously thinning the overburden 1206 (FIG.12) and removing any superfill 1208 of the first conductive layer 1202.The flexible material 1200 can be removed after the pre-planarizedsurface 1302 has been completed. Thereafter, additional planarization ofthe first and second conductive layers 1202 and 1300 can be performed toelectrically isolate the conductive materials in the wide and narrowfeatures. In those embodiments in which the first conductive layer 1202does not completely fill the wide trench 106, planarizing the secondconductive layer 1300 does not completely remove the second conductivelayer 1300 and a structure is produced such as the one shown in FIG. 8.In those embodiments in which the first conductive layer 1202 doescompletely fill the wide trench 106, planarizing the second conductivelayer 1300 removes the entire second conductive layer 1300 and astructure is produced such as the one shown in FIG. 11.

FIGS. 14-19 further illustrate various apparatus embodiments of theinvention. FIG. 14 shows a side elevation view of a partialcross-section of one embodiment of an apparatus 1400 for producing apre-planarized surface. The apparatus 1400 includes a wafer support 1402(in cross-section) for securing a wafer 1404 (in cross-section) duringprocessing. The apparatus 1400 also includes a workpiece 1406 (incross-section) that in this embodiment includes a reservoir 1408 and aporous membrane 1410. A support structure 1412 supports the workpiece1406 relative to the wafer 1404.

The wafer support 1402 secures the wafer 1404. In some embodiments thewafer support 1402 is a vacuum chuck. In some embodiments the wafersupport 1402 is rotatable around an axis 1414 as shown in FIG. 14, whilein other embodiments the wafer support 1402 is non-rotatable. Rotationof the wafer support 1402 is one method for introducing a relativelateral motion between the workpiece 1406 and the wafer 1404.

The support structure 1412 supports the workpiece 1406 relative to thewafer 1404. Accordingly, the support structure 1412 includes anengagement mechanism 1416 to adjust a spacing between the workpiece 1406and the wafer 1404. The engagement mechanism 1416 lowers the workpiece1406 until the porous membrane 1410 is in contact with the wafer 1404.In some embodiments, the engagement mechanism 1416 continues to lowerthe workpiece 1406 until a slight pressure is developed between theworkpiece 1406 and the wafer 1404. Once the pre-planarized surface iscompleted, the engagement mechanism 1416 raises the workpiece 1406 offof the wafer 1404. Alternatively, rather than moving the workpiece 1406,an alternative engagement mechanism (not shown) can be used to raise andlower the wafer support 1402. Various mechanisms suitable for engagementmechanism 1416 are well known in the art and include, for example, aspindle assembly. In some embodiments, the support structure 1412 alsoincludes means for introducing a relative lateral motion between theworkpiece 1406 and the wafer 1404 as will be described with respect toFIGS. 15-17. Further variations include placing the workpiece 1406 onthe bottom and locating the wafer support 1402 on the top.

As noted, the workpiece 1406 in this embodiment includes a reservoir1408 and a porous membrane 1410. In some embodiments the porous membrane1410 is replaced by some other flexible material 1200 (FIG. 12). Theporous membrane 1410 spans an open side of the workpiece 1406 that facesthe reservoir 1408. Accordingly, the reservoir 1408 can be filled with asolution and then pressurized to force the solution out through theporous membrane 1410. In some embodiments the flow through the porousmembrane 1410 is about 5 to about 500 ml/min. In some embodiments thereservoir 1408 is pressurized to about 5 to about 50 psi.

Numerous techniques are well known in the art for pressurizing areservoir and can be adapted to the present invention. For example, insome embodiments the reservoir 1408 is partially filled with thesolution and then a compressed gas (e.g., air, N₂, Ar, etc.) isintroduced above the level of the solution until the desired pressure isobtained. In other embodiments a syringe pump delivers the solution tothe reservoir 1408 at the desired pressure. Similarly, in otherembodiments a diaphragm pump having a pressure-regulated flow deliversthe solution to the reservoir 1408. In still other embodiments thesolution is delivered from a pressurized canister that contains abladder filled with the solution. As the canister is pressurized with acompressed gas the pressure within the bladder increases, driving thesolution out of the bladder and into the reservoir 1408.

FIG. 15 shows a top plan view of the apparatus of FIG. 14. As can beseen from the perspective shown in FIG. 15, although the workpiece 1406covers an area that is smaller than an area of the wafer 1404, relativelateral motion between the workpiece 1406 and the wafer 1404 can assurethat the workpiece 1406 makes contact with most or all of the entirearea of the wafer 1404 during the formation of a pre-planarized surface.The relative lateral motion can be introduced in many different ways.For example, rotation 1500 of the wafer 1404 around axis 1414 (FIG. 14)can be achieved by mounting the wafer support 1402 on a spindle that isrotated by a drive mechanism.

Additional relative lateral motions can be introduced through theworkpiece 1406, for example by rotation 1502 of the workpiece 1406.Further relative lateral motions can be introduced by laterallytranslating the workpiece 1406. Two types of lateral translationalmotions are indicated by FIG. 15, reciprocal translation 1504 and lineartranslation 1506. Linear translation 1506 can be achieved, for example,by extending an arm 1508 that supports the workpiece 1406 as shown, orby linearly translating the wafer 1404 beneath the workpiece 1406. Thelatter can be achieved, for instance, by placing the wafer support 1402on a reciprocating assembly having linear bearings. Additional relativelateral motions can be introduced by vibrating either or both of theworkpiece 1406 and the wafer 1404. It will be appreciated that variouscombinations of the several relative lateral motions can also be usedincluding orbital motions.

As noted herein, for embodiments in which the workpiece 1406 has asmaller area than the area of the wafer 1404, the relative lateralmotion between the workpiece 1406 and the wafer 1404 can assure that themethod of forming a pre-planarized surface is applied to the entire areaof the wafer 1404. It should also be noted that in these and otherembodiments relative lateral motions can also improve the flow rate ofthe solution through the porous membrane 1410 (FIG. 14) and improve masstransport within cavities as the second conductive layer is deposited.Specifically, relative lateral motion, such as vibration, can improvecirculation within cavities to help move fresh solution to, and movedepleted solution and waste products away from, a growing layer of thesecond conductive material.

FIG. 16 shows a top plan view of an apparatus according to anotherembodiment of the present invention. The embodiment illustrated in FIG.16 is similar to that described with respect to FIG. 15, however in theembodiment of FIG. 16 the workpiece 1600 has a larger area than that ofthe wafer 1404 and therefore the workpiece 1600 can contact the entirewafer area at any given time. Relative lateral motion can be introducedbetween the workpiece 1600 and the wafer 1404 by rotating either or bothof the workpiece 1600 and wafer 1404. Other relative lateral motionsnoted with respect to FIG. 15 such as vibration can also be employed. Itwill be appreciated that since the area of the workpiece 1600 is greaterthan the area of the wafer 1404, the workpiece 1600 can take a shapeother than the circular shape shown in FIG. 16.

FIG. 17 shows a top plan view of an apparatus according to still anotherembodiment of the present invention. The embodiment illustrated in FIG.17 is similar to that described with respect to FIGS. 15 and 16, howeverin the embodiment of FIG. 17 the workpiece 1700 has an area equal to, orslightly smaller than, that of the wafer 1404. Where the area of theworkpiece 1700 is smaller than that of the wafer 1404, a small relativelateral motion such as by vibration or orbital oscillation can assurethat the workpiece 1700 forms a pre-planarized surface across the entirearea of the wafer 1404. Other forms of relative lateral motion describedelsewhere herein can also be employed.

FIG. 18 shows a cross-section of another embodiment of an apparatus 1800for producing a pre-planarized surface. The apparatus 1800 includes awafer support 1402 for securing a wafer 1404 during processing. Theapparatus 1800 also includes a workpiece 1806 that in this embodimentincludes a poromeric material 1808. A support structure (not shown)holds the wafer support 1402 relative to the workpiece 1806 and allowsthe workpiece 1806 to be brought into contact with the wafer 1404, muchas the support structure 1412 (FIG. 14) supports the workpiece 1406relative to the wafer support 1402. Although the workpiece 1806 is shownas being below the wafer 1404 in FIG. 18, it will be understood that theworkpiece 1806 can alternately be positioned above the wafer 1404.

FIG. 19 shows a side elevation view of an apparatus 1900 that is onepossible variation of apparatus 1800 (FIG. 18). In apparatus 1900, theflexible material is provided as a continuous loop 1902 around a pair ofrollers 1904. A support structure (not shown) allows the wafer 1404(FIG. 18) to be brought into contact with the continuous loop 1902, orvice-versa. A linear relative lateral motion is achieved in thisembodiment by driving the continuous loop 1902 around the pair ofrollers 1904. Additional relative lateral motion can be achieved byrotating the wafer support 1402, as shown. Further relative lateralmotions can be introduced by applying other motions to the wafer support1402, such as vibration and orbital motion, as described elsewhereherein. Although the poromeric material is provided as a continuous loop1902 in this embodiment, it will be appreciated that in otherembodiments the poromeric material can take other forms, such as a diskor a rectangle. In some embodiments the poromeric material includesraised edges to contain the electroless solution.

In the embodiments shown in FIGS. 18 and 19, a surface of the poromericmaterial is wetted by a solution 1906. The solution 1906 is then carriedby the poromeric material to the wafer 1404 (FIG. 18). Although FIG. 19shows solution 1906 being dripped or sprayed onto the continuous loop1902, other methods for delivering the solution 1906 to the surface of aporomeric material can also be used. For example, one roller 1904 can beimmersed in a reservoir of the solution.

In the foregoing specification, the invention is described withreference to specific embodiments thereof, but those skilled in the artwill recognize that the invention is not limited thereto. Variousfeatures and aspects of the above-described invention may be usedindividually or jointly. Further, the invention can be utilized in anynumber of environments and applications beyond those described hereinwithout departing from the broader spirit and scope of thespecification. The specification and drawings are, accordingly, to beregarded as illustrative rather than restrictive.

1. A method for producing a planarized surface, comprising: providing asubstrate having a narrow feature and a wide feature defined therein;forming a first layer above the substrate, the first layer filling thenarrow feature at least partially filling the wide feature, and having acavity defined therein and aligned with the wide feature; forming asacrificial layer in the cavity; and removing at least some of the firstand sacrificial layers together in a planarization process.
 2. Themethod of claim 1 wherein forming the sacrificial layer includescontacting a flexible material with the first layer, and introducing arelative lateral motion between the flexible material and the firstlayer.
 3. The method of claim 2 wherein the relative lateral motionincludes a rotational component.
 4. The method of claim 2 wherein therelative lateral motion includes a vibrational component.
 5. The methodof claim 2 wherein the relative lateral motion includes an orbitalcomponent.
 6. The method of claim 1 wherein the first layer completelyfills the wide feature and removing at least some of the first andsacrificial layers includes completely removing the sacrificial layer.7. The method of claim 1 wherein removing at least some of the first andsacrificial layers does not completely remove the sacrificial layer. 8.The method of claim 1 wherein removing at least some of the first andsacrificial layers includes a stress-free planarization.
 9. The methodof claim 1 wherein removing at least some of the first and sacrificiallayers includes a Chemical Mechanical Planarization.
 10. The method ofclaim 1 wherein removing at least some of the first and sacrificiallayers includes exposing the substrate between the narrow and widefeatures.
 11. A method for producing a planarized surface, comprising:providing a substrate including a narrow feature and a wide feature;forming a first layer above the substrate, the first layer filling thenarrow feature, at least partially filling the wide feature, andincluding a cavity aligned with the wide feature; contacting a flexiblematerial with at least a portion of the first layer; using the flexiblematerial to deliver a solution to the cavity; forming a sacrificiallayer in the cavity from the solution; and removing portions of thefirst layer and sacrificial layer.
 12. The method of claim 11 whereinthe substrate includes a dielectric material with a dielectric constantless than a dielectric constant of SiO₂.
 13. The method of claim 12wherein the dielectric material includes OSG, FSG, or a low-k material.14. The method of claim 11 wherein the narrow feature has a lateraldimension of about 100 mm or less.
 15. The method of claim 11 whereinthe wide feature has a lateral dimension greater than about 100 nm. 16.The method of claim 15 wherein the wide feature has a lateral dimensionof about 500 μm.
 17. The method of claim 11 wherein forming the firstlayer includes forming a first conductive layer by electrochemicallydepositing a conductive copper material.
 18. (canceled)
 19. (canceled)20. The method of claim 11 wherein the flexible member includes a porousmembrane.
 21. The method of claim 20 further comprising pressurizing areservoir containing the solution and adjoining the membrane on a sideopposite a side contacting the first layer.
 22. The method of claim 20wherein the porous membrane includes a combination of polyurethane andan abrasive.
 23. The method of claim 20 further comprising introducing arelative lateral motion between the porous membrane and the substrate.24. The method of claim 23 wherein the porous membrane is effective topolish the portion of the first layer.
 25. (canceled)
 26. The method ofclaim 11 wherein the flexible material includes a poromeric materialincluding a closed-cell structure with open pores exposed at a surfacethereof.
 27. (canceled)
 28. The method of claim 26 further comprisingwetting the poromeric material with the solution.
 29. The method ofclaim 26 wherein delivering the solution to the cavity includesdeveloping a pressure between the poromeric material and the firstlayer.
 30. The method of claim 26 wherein delivering the solution to thecavity includes introducing a relative lateral motion between thesubstrate and the poromeric material.
 31. The method of claim 11 whereinthe solution includes an electroless plating solution.
 32. The method ofclaim 11 wherein forming the second sacrificial layer includes forming asecond conductive layer.
 33. The method of claim 32 wherein forming thesecond conductive layer includes an electroless deposition of aconductive material.
 34. The method of claim 33 wherein the conductivematerial is copper.
 35. The method of claim 11 wherein removing portionsof the first and sacrificial layers includes applying a stress-freepolishing technique.
 36. The method of claim 11 wherein forming thefirst layer includes completely filling the wide feature.
 37. The methodof claim 36 wherein the first layer forms an overfill above the widefeature that extends about 10% to about 20% of a depth of the widefeature above a level of a top surface of the substrate.
 38. The methodof claim 36 wherein removing portions of the first and sacrificiallayers includes removing the sacrificial layer.
 39. The method of claim11 wherein forming the first layer includes filling less than the entirewide feature.
 40. The method of claim 39 wherein about 10% to about 30%of a depth of the wide feature is filled by the first layer.
 41. Themethod of claim 39 wherein removing portions of the first andsacrificial layers includes removing less than the entire sacrificiallayer.
 42. The method of claim 11 wherein the first and sacrificiallayers are formed of the same conductive material.
 43. The method ofclaim 11 wherein contacting the flexible material with at least theportion of the first layer inhibits the deposition of the sacrificiallayer above an overburden of the first layer.
 44. An apparatus forproducing a planarized surface, comprising: a wafer support for securinga wafer having an area; a workpiece including a reservoir containing anelectroless plating solution and having a flexible and porous membranespanning a side; an engagement mechanism capable of bringing theworkpiece and the wafer into contact with each other; and means forintroducing a relative lateral motion between the workpiece and thewafer.
 45. The apparatus of claim 44 wherein the reservoir ispressurizable.
 46. The apparatus of claim 44 wherein the porous membranehas an area less than the area of the wafer.
 47. The apparatus of claim46 wherein the means for introducing relative lateral motion includesmeans for linearly translating the workpiece.
 48. The apparatus of claim47 wherein the means for introducing relative lateral motion furtherincludes means for rotating the workpiece around an axis.
 49. Theapparatus of claim 46 wherein the means for introducing relative lateralmotion includes means for rotating the wafer support around an axis. 50.The apparatus of claim 46 wherein the means for introducing relativelateral motion includes means for vibrating the workpiece.
 51. Theapparatus of claim 44 wherein the porous membrane has an area equal toor larger than the area of the wafer.
 52. The apparatus of claim 51wherein the means for introducing relative lateral motion includes meansfor rotating the wafer support around an axis.
 53. The apparatus ofclaim 51 wherein the means for introducing relative lateral motionincludes means for rotating the workpiece around an axis.
 54. Theapparatus of claim 44 wherein the wafer support is a vacuum chuck. 55.The apparatus of claim 44 wherein the porous membrane includespolyurethane.
 56. The apparatus of claim 44 wherein the porous membraneincludes a fluorocarbon material.
 57. The apparatus of claim 44 whereinthe porous membrane includes a sintered polymeric material.
 58. Theapparatus of claim 44 wherein the porous membrane includes a ceramic.59. The apparatus of claim 44 wherein the porous membrane has athickness between about 0.1 mm to about 3.0 mm.
 60. The apparatus ofclaim 44 wherein the porous membrane includes open-cell pore structure.61. The apparatus of claim 44 wherein the porous membrane includes anumber of holes disposed therethrough.
 62. The apparatus of claim 44wherein the porous membrane includes an amount of porosity between about5% to about 50%.
 63. The apparatus of claim 44 wherein the porousmembrane includes an amount of porosity between about 10% to about 20%.64. The apparatus of claim 44 wherein the porous membrane includes anabrasive. 65-75. (canceled)